Sensitivity to light is the inability to tolerate light, medically known as photophobia. In someone who is light sensitive, any type of light source (sunlight, fluorescent light, incandescent light) can cause discomfort. Photophobia typically causes a need to squint or close the eyes, and headache, nausea, or other symptoms may be associated with photophobia. Symptoms may be worse with bright light. Light sensitivity is caused by a number of conditions that affect the eye (such as iritis, uveitis, and keratitis), as well as conditions that affect the entire body.
Uveitis is inflammation of the uvea of the eye. The uvea is made up of three parts. The first part is the iris, which is the colored ring of tissue you can see in the mirror. The dark hole in the middle of the iris is the pupil. The second and third parts, which you cannot see directly when looking in a mirror, are the ciliary body and the choroid. They are located behind the iris. An ophthalmologist can visualize them using special examination equipment.
Inflammation of the iris is called iritis. Inflammation of the ciliary body is called intermediate uveitis or cyclitis. Inflammation of the choroid is called choroiditis (or chorioretinitis if the retina is also involved). Inflammation of all three is called panuveitis.